The present invention relates to microporous glass waveguides doped with selected materials, and more particularly to such glass waveguides for fibre optic applications.
Many different devices have been proposed to control the property of light in optical materials, such as the polarization state, the phase or the intensity, particularly for application in optical fibre telecommunications. Among these different devices, a class of them use the property that electro-optic materials have to change the index of refraction upon application of an electric field. These latter devices are based on the principle of controlling the phase of the light travelling through the device, and have many applications. For example, in a Mach-Zender type interferometer configuration, the power transmitted can be controlled by modulating the phase of the light travelling in one of the arms of the interferometer.
To the inventors"" knowledge, devices using electro-optic materials are limited to planar waveguides, which poses two fundamental problems when trying to couple them to optical fibres. First, the index profile of a planar waveguide does not possess the circular symmetry of an optical fibre index profile, which results in coupling losses between the two waveguides, as well as a polarization dependence on the transmission properties. Secondly, the planar and voluminous structure of a planar waveguide does not permit an easy alignment of the core of the planar waveguide with the core of the optical fibre, increasing the costs. One could also add that in some cases, the index of refraction of the planar waveguide is considerably greater than that of the optical fibre, which causes problems due to Fresnel reflections. This is particularly true with planar waveguides inscribed in lithium niobate, whose index is 2.12, compared to 1.45 for silica.
On the other hand, two optical fibres can be very precisely aligned by using inexpensive connectors, or by splicing two fibres with a splicer, the cost of which is quickly amortized. Furthermore, aligning two optical fibres does not cause Fresnel reflections.
Other than electro-optic phase modulators, two devices, among others, which find particular application in the field of telecommunications are polarizers and Bragg gratings. Existing polarizers are limited to single mode waveguides and Bragg gratings present limited diffraction efficiencies. These limits are related to the manufacturing process or to the material used for the manufacture of waveguides, i.e. silica in the case of optical fibres.
Other materials, such as polymers, have advantages over silica, such as optical activity, induced dichroism and a high diffraction efficiency. It would thus be useful to incorporate such materials into optical fibers.
Finally, another device which finds particular use in the telecommunications field is an optical isolator, of which one of the components is a Faraday rotator. These devices work in a magnetic field created by a magnet, and it would be useful to insert the magnet and materials exhibiting a high Faraday effect into the waveguides themselves.
It is thus an object of the present invention to provide a porous waveguide including a material which exhibits optical properties. In accordance with the invention, this object is achieved with an optical waveguide made of porous glass, wherein at least a portion of the pores of the porous glass are filled with an optical material.
In accordance with another aspect of the invention, there is provided an optical waveguide apparatus comprising: an optical waveguide made of porous glass, where the pores of the porous glass are filled with an optical material; and a pair of electrodes on opposed sides of the optical waveguide in order to induce a change in the index of refraction of the optical waveguide upon application of an electric field between the electrodes.
In an advantageous aspect of the invention, the optical material is a polymer or other type of material exhibiting electro-optical properties.
The devices according to the present invention can be used as phase modulators.